Thermal receiver for high power solar concentrators and method of assembly

ABSTRACT

A device for dissipating heat from a photovoltaic cell is disclosed. A first thermally conductive layer receives heat from the photovoltaic cell and reduces a density of the received heat. A second thermally conductive layer conducts heat from the first thermally conductive layer to a surrounding environment. An electrically isolating layer thermally couples the first thermally conductive layer and the second thermally conductive layer.

BACKGROUND

The present disclosure relates to solar energy, and more specifically,to dissipating heat from photovoltaic cells illuminated by concentratedsolar rays.

Solar power concentrators are often used in photovoltaic systems toincrease an output of the photovoltaic cells. New solar concentratorsare able to increase a concentration of incident solar energy by up toand beyond 2000 times. A consequence of this concentration is theproduction of high levels of heat which raises the temperatures of solarcells. However, solar cells must be operated at temperatures that aretypically less than about 110° C. in order to prevent heat damage.Another consequence of the solar concentration is a large currentdensity. It is desired to couple this current to a load in a manner thatoffers as little electrical resistance as possible to avoid dissipatingelectrical energy as heat.

SUMMARY

According to one embodiment of the present disclosure, a device fordissipating heat from a photovoltaic cell includes: a first thermallyconductive layer configured to receive heat from the photovoltaic celland reduce a density of the received heat; a second thermally conductivelayer configured to conduct heat from the first thermally conductivelayer to a surrounding environment; and an electrically isolating layerconfigured to thermally couple the first thermally conductive layer andthe second thermally conductive layer.

According to another embodiment of the present disclosure, aphotovoltaic cell assembly includes: a photovoltaic cell; a firstthermally conductive layer configured to receive heat from thephotovoltaic cell and reduce a density of the received heat; a secondthermally conductive layer configured to conduct heat from the firstthermally conductive layer to a surrounding environment; and anelectrically isolating layer configured to thermally couple the firstthermally conductive layer and the second thermally conductive layer.

According to another embodiment of the present disclosure, a solar panelincludes: a plurality of photovoltaic cell assemblies; at least one wirecoupling the photovoltaic cell assemblies; wherein a photovoltaic cellassembly selected from the plurality of photovoltaic cell assembliesincludes: a photovoltaic cell, a first thermally conductive layerconfigured to receive heat from the photovoltaic cell and reduce adensity of the received heat, a second thermally conductive layerconfigured to conduct heat from the first thermally conductive layer toa surrounding environment, and an electrically isolating layerconfigured to thermally couple the first thermally conductive layer andthe second thermally conductive layer.

Additional features and advantages are realized through the techniquesof the present disclosure. Other embodiments and aspects of thedisclosure are described in detail herein and are considered a part ofthe claimed disclosure. For a better understanding of the disclosurewith the advantages and the features, refer to the description and tothe drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the disclosure is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe disclosure are apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 shows a photovoltaic assembly according to an exemplaryembodiment of the present disclosure;

FIG. 2 shows an exploded view of an exemplary cell package of thephotovoltaic assembly FIG. 1 in one embodiment of the presentdisclosure;

FIG. 3 shows an alternate embodiment of a cell package of thephotovoltaic assembly of FIG. 1;

FIG. 4 shows a cross-sectional view of an exemplary photovoltaicassembly coupled to a backplane;

FIG. 5 shows an exemplary assembly for mounting a plurality ofphotovoltaic assemblies;

FIG. 6 shows a top view of a solar panel assembly in an exemplaryembodiment;

FIG. 7 shows an exemplary solar panel package of the present disclosure;and

FIG. 8 shows an exploded view of the solar panel package of FIG. 7.

DETAILED DESCRIPTION

FIG. 1 shows a photovoltaic assembly 100 according to an exemplaryembodiment of the present disclosure. The exemplary photovoltaicassembly 100 includes an optical assembly 106 that is affixed to a frontsurface of a photovoltaic cell 102 for concentrating solar rays. In anexemplary embodiment, the optical assembly 106 provides a concentrationof about 1600 times or greater than the incident solar concentration. Inan exemplary embodiment, this level of solar concentration produces alarge amount of heating at the photovoltaic cell 102. The photovoltaiccell 102 is coupled to a cell package 104 for dissipating heat from thephotovoltaic cell 102. In an exemplary embodiment, a back surface of thephotovoltaic cell 102 is directly soldered to the cell package 104 usinga solder. The solder may include an 80/20 lead/tin solder or a low meltsolder. Alternate solders usable for soldering the photovoltaic cell 102and cell package 104 may include alloys containing at least one of lead,tin, copper, gallium, silver, manganese, magnesium, bismuth, indium,zinc and antimony, such as for example Sn—Ag—Cu, Sn—Ag—Cu—Zn andSn—Ag—Cu—Mn. Alternately, the photovoltaic cell 102 may be coupled tothe cell assembly 104 using a conductive particle infused polymeradhesive, such as silver paste. Wires 108 are bonded between thephotovoltaic cell 102 and the cell package 104 to provide an electricalpath for current produced at the photovoltaic cell 102. In an exemplaryembodiment, the wires 108 may be bonded using a solder such as theexemplary solders listed above. In an alternate embodiment the cell isconnected to the top surface conductors on the cell package using on ofwire bonding and ribbon bonding methods where the wire and ribbon maycomprise one of gold, silver, platinum, palladium, aluminum, silicon andcopper.

FIG. 2 shows an exploded view of an exemplary cell package 104 of FIG. 1in one embodiment of the present disclosure. The exemplary cell package104 includes a coating 202, a solder mask 204, a copper layer 206, adielectric layer 208 and a substrate layer 210. In an exemplaryembodiment, copper layer 206 and substrate layer 210 form electrodescoupled to the photovoltaic cell 102. In an exemplary embodiment, copperlayer 206 forms an electrical circuit with the photovoltaic cell 102.

Coating 202 provides a top surface of the cell package and is in contactwith the photovoltaic cell 102. Coating 202 provides a substantiallycorrosion resistant surface for wire bonding and may include at leastone of gold, silver, nickel, zinc and tin. Solder mask 204 provides asecond layer of the cell package 104 and includes an insulatingmaterial. The solder mask may include standard solder mask material suchas, for example, an epoxy paint. The solder mask 204 may be applied viascreen printing in an exemplary embodiment. The solder mask may havewindows for wire bonding, strap bonding or strap welding of connectionsbetween the photovoltaic cell 102 and package electrodes (not shown) ofthe cell package 104. The solder mask 204 further includes windowsallowing interconnecting wires (see FIG. 5) to be soldered to thepackage electrodes, thereby interconnecting a plurality of photovoltaicassemblies 100 to each other and/or to an external device. In exemplaryembodiments, the interconnecting wires may be bonded between thephotovoltaic cell 102 and the electrodes of the cell package 104 usinggold wire bonding, ribbon bonding or strap welding, for example.Connective bonding material may include at least one of gold, silver,Invar, iron, copper and tin.

Copper layer 206 provides a third layer of the cell package 104 and isan electrically conductive layer that forms a second electrode of thephotovoltaic cell 104. In alternate embodiments, the copper layer 206may be made of any material that is electrically conductive. Copperlayer 206 may be patterned using exemplary lithographic methods such asphotolithography, screen printing, and ink jet printing, for example.After patterning, an etch process may be used to remove unwanted copperfrom the copper layer 206 to form a selected shape. In addition, thecopper layer is selected to provide an electrically conductive channelfor conducting current generated from the photovoltaic cell, forexample, to the interconnecting wires. In various embodiments, thecurrent densities are in a range from about 6.3 amps per squarecentimeter (amps/cm²) to about 25.2 amp/cm². The copper layer 206 may beelectrically coupled to an electrode of the photovoltaic cell 102 usinga ribbon bond, a wire bond, etc.

Dielectric layer 208 provides a fourth layer of the cell package 104that provides electrical isolation of the copper layer 206 from theunderlying substrate layer 210. The dielectric layer 208 further allowsheat transfer from the copper layer 206 to the substrate layer 210. Inan exemplary embodiment, the dielectric layer 208 may include an FR4matrix of glass fiber and epoxy that may be cured by thermal, chemicalor ultraviolet methods.

Substrate layer 210 provides a fifth and bottom layer of the cellpackage 104 and may be a thick layer in comparison to layers 202-208.The substrate layer 210 may serve as both an electrode and a thermalconductor. Increasing the thickness d of the substrate layer 210relative to the thicknesses of layers 202-208 increases an ability ofthe substrate layer 210 to spread the heat conducted to the substratelayer from the photovoltaic cell 104 via the layers 202-208. Thesubstrate layer may have lateral dimensions of length and width.Increasing the size of the lateral dimensions may improve a thermalcoupling of the substrate layer 210 to a backplane (see FIG. 4). Thelateral dimension and thickness of the substrate layer may be selectedto achieve a selected thermal performance (i.e., solar heat dissipation)of the cell package 104 and a selected operating temperature of therelated photovoltaic assembly 100. In an exemplary embodiment, thesubstrate layer 210 is made of copper or other material selected toachieve high thermal conductivity. In alternate embodiments, layer 210may include aluminum or at least one of copper, aluminum, iron, chrome,nickel, molybdenum, zinc and tin. In an embodiment in which aphotovoltaic cell has a length and width of about 3.75 millimeters (mm),a length and width of the substrate layer 210 may be about 15 mm and thethickness may be about 1.5 mm.

Layers 206, 208 and 210 may be coupled to each other by pressure andheat to cure layer 208 to form a bond. In an exemplary embodiment,layers 206, 208 and 210 may be bonded to form a sheet that is thenseparated into individual substrates suitable for use in a selected cellpackage 104. The separated substrates may be patterned into individualsubstrate layers using printed circuit methods.

FIG. 3 shows a cell package 104 in an alternate embodiment. Thealternate cell package 104 includes a coating 302, a solder mask 304, acopper layer 306, a dielectric layer 308 and a substrate layer 310. Inthe alternate embodiment, layer 306 includes both cell electrodes 306 aand 306 b coupled to the photovoltaic cell 102 and is made of thickcopper that has a thickness that is substantially between about 20microns and about 400 microns. The dimensions of the layer 306 areselected so as to be conducive to spreading heat laterally. Layer 308 ismade thin in comparison to layer 208 of FIG. 2 to increase heat transferbetween layer 306 and the substrate 310.

FIG. 4 shows a cross-sectional view 400 of an exemplary photovoltaicassembly coupled to a backplane 410. The photovoltaic assembly includesphotovoltaic cell 402 mounted on an exemplary cell package 404. The cellpackage 404 is coupled to an insulation layer or layers 408 via athermal adhesive 406 that allows heat transfer between the cell package404 and the insulation layer or layers 408. The insulation layer orlayers 408 may be a printable layer. In one embodiment, the insulationlayer or layers 408 may be multi-layer insulators. The insulation layeror layer 408 may also include aluminum oxide, polymers, or otherelectrically resistive particles, etc.

In an exemplary embodiment, the thermal adhesive 406 may include amaterial having at least one of a high thermal conductivity, a highmechanical flexibility, an ability to cure at low temperatures, anability to withstand operating temperatures in a range from about −40°C. to about 120° C., and an ability to adhere to the contacting faces ofthe cell package 404 and of the insulation layer or layers 408 providingelectrical insulation. The thermal adhesive 406 may include, but is notlimited to, SilCool® TIA-0220 of Momentive Performance Materials, Inc.In an exemplary embodiment, the thermal adhesive 406 includes aninsulating silicone adhesive. In alternate embodiments, the thermaladhesive 406 may include epoxy and acrylic adhesives. In anotherembodiment, the thermal adhesive 406 includes a polymer with thermallyconductive particles embedded therein. Exemplary polymers may include atleast one of silicone, acrylic and epoxy. Exemplary particles mayinclude at least one of aluminum oxide, aluminum nitride and silicondioxide. In an exemplary embodiment, the thermal adhesive 406 iscompressed to a thin bond line of approximately 50 microns or less andis allowed to slightly extrude beyond the edges of the cell package 404.

The insulation layer 408 or layers reduces electrical conduction betweenthe cell package 404 and the backplane 410, while allowing heat transfertherebetween. The insulation layer or layers 408 may be bonded to analuminum backplane 410 prior to bonding the insulation layer or layers408 to the cell package 404. The insulation layer or layers 408 mayinclude an epoxy-based screen-printable material. In variousembodiments, the insulation layer or layers 408 may include anyelectrically-insulating material with high dielectric strength, strongadhesion to the anodized aluminum of the backplane 410 and an ability toresist heat damage at temperatures in an operating range from about 85°C. to about 120° C. In an exemplary embodiment, the insulation layer orlayers 408 may include TechniFlex by Technic Corp. and may be appliedusing screen printing methods on the backplane 410 to a thickness ofabout 15 microns. In alternative embodiments, the insulation layer orlayers 408 may include, but is not limited to, paints, lacquers, powdercoats, etc. Such materials in the alternative embodiment of theinsulation layer or layers 408 may include at least one of polyester,polyurethane, polyester-epoxy, epoxy, acrylic and silicone.

The aluminum backplane 410 may include a sheet of anodized aluminum. Inan exemplary embodiment, the backplane 410 includes a sheet of about 1.5mm in thickness and an anodized layer thickness of about 10 microns. Invarious embodiments, the anodized layer may have a thickness thatprovides a protective layer to the aluminum surface as well as anelectrical breakdown resistance. Electrical breakdown resistance isprovided by the thermal adhesive 406, the insulation layer or layers 408and the anodization of the backplane 410.

In an exemplary operation of the photovoltaic assembly, heatconcentrated at the photovoltaic cell is transferred to the cell package404. At the cell package 404, the heat is distributed in along lateraldimensions of the cell package at the copper substrate, such assubstrate 210 in FIG. 2 or alternately substrate 310 in FIG. 3 in orderto reduce an areal density of the heat by spreading the heat, in generalalong a lateral dimension of the substrate. Heat from the substrate 210is transferred to the aluminum backplane 410 through the insulationlayer 408. In various embodiments, the insulation layer 408 preventscurrent transfer between substrate 310 and the aluminum backplane 410 byproviding a breakdown resistance to about 1700 volts or more.

FIG. 5 shows an exemplary assembly 500 for mounting a plurality ofphotovoltaic assemblies. Cell package 502 a is shown having anassociated photovoltaic cell 504 a and an associated secondary optic 506a. Cell package 502 b is shown having an associated photovoltaic cell504 b and an associated secondary optic 506 b. Cell packages 502 a and502 b are coupled to the aluminum backplane 510 via exemplaryscreen-printed dielectric 520. Cell packages 502 a and 502 b aredisposed on the backplane 510 at a location that corresponds to a focalpoint of their respective secondary optics 506 a and 506 b when thebackplane 501 is perpendicular to solar radiation. In one embodiment, aprotection diode 512 is packaged to the backplane in a manner similar tothe packaging of cell packages 502 a and 502 b. The protection diode 512includes a heat shield 514 that protects the protection diode 512 fromheat or dissipates heat from the protection diode 512. In an exemplaryembodiment, the heat shield 514 includes a copper strip that covers theprotection diode 512 and is soldered to contact pads of the diodepackage.

Interconnecting wiring 516 provides an electrical connection betweencell packages 502 a and 502 b. In one embodiment, the interconnectingwiring 516 connects printed circuit layers of the cell packages 502 aand 502 b. The interconnecting wiring 516 includes copper wire that issoldered to electrodes of the cell packages 502 a and 502 b. Thediameter of the wire is selected to handle a current provided by theexemplary cell packages and to reduce internal resistance losses Kinks518 are introduced into the interconnecting wiring 516 to avoidmechanical stress due to thermal expansion of the interconnecting wiring516. The interconnecting wiring 516 may be sufficiently rigid to beself-supporting. The interconnecting wiring 516 may be affixed to thebackplane 510 separated by a separation distance in a range of about 1millimeter to about 2 millimeters above the surface of the backplane510. Such a configuration avoids physical contact with the insulatingdielectric or with the aluminum anodized surface.

FIG. 6 shows a top view of a solar panel assembly 600 in an exemplaryembodiment. The exemplary solar panel assembly 600 includes five tiers602 a-602 e of cell packages. In each tier, four cell packages, such asexemplary cell packages 604 a-604 d, and a protection diode 606 areconnected in parallel using the interconnecting wiring 608. The cellpackages are coupled to an aluminum backplane 610 via dielectric layer612. The tiers 602 a-602 e are connected in series to form a solar panelassembly 600 having 20 cell packages. In various embodiments, the numberof cells in parallel vs. the number of cells in series may be selectedto achieve a selected current-voltage ratio of the solar panel assembly600. Having cells wired in parallel (in the tiers) allows one or morecells to fail while maintaining the function of the panel at a reducedpower, thereby improving an overall reliability of the solar panelassembly 600. Terminal connections 614 provide electrical coupling fromthe interconnecting wiring 608 to external circuitry. The interconnectwiring 608 may be soldered to an insulated multi-strand copper externalconnection wire (not shown) that penetrates the aluminum backplane 610to an exterior of the solar panel assembly 600 via a strain relief cordgrip.

FIG. 7 shows an exemplary solar panel package 700 of the presentdisclosure. The exemplary solar panel package 700 includes an enclosure702 that encloses a solar panel assembly (not shown) having one or morecell packages according to the present disclosure. A lens 704 such as aFresnel lens is coupled to a top of the enclosure 702 using an adhesive,to enclose the solar panel assembly. In various embodiments, theadhesive includes a silicone adhesive. Filtered vents are provided inthe enclosure 702 to equalize pressures between an interior and anexterior of the enclosure 702 and to allow moisture within the enclosureto escape to an exterior of the enclosure 702.

FIG. 8 shows an exploded view 800 of the solar panel package 700 of FIG.7. The exploded view 800 shows the enclosure 702 and the Fresnel lens804. Additionally, the exploded view 800 shows the solar panel assembly802 that includes a number of cell packages and resides in a chamberformed by the enclosure 702 and the Fresnel lens 704. The enclosure 702may further include one or more cooling fins 804 to aid in thedispersion of heat from the enclosure 802 and thus from the solar panel802.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the disclosure. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed disclosure.

While the exemplary embodiment to the disclosure had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the disclosure first described.

What is claimed is:
 1. A method of dissipating heat from a photovoltaiccell, comprising: coupling the photovoltaic cell to a first thermallyconductive layer; coupling the first thermally conductive layer to anelectrically isolating layer; and coupling the electrically isolatinglayer to a second thermally conductive layer; wherein the firstthermally conductive layer reduces a density of received heat from thephotovoltaic cell and conducts the heat to the second thermallyconductive layer via the electrically isolating layer.
 2. The method ofclaim 1, wherein reducing the heat density in the first thermallyconductive layer further comprising spreading heat over a lateral areaof the first thermally conductive layer.
 3. The method of claim 1,further comprising conducting electricity from the photovoltaic cell inthe first thermally conductive layer.
 4. The method of claim 1, furthercomprising coupling a thermally conducting backplane to the secondthermally conductive layer to conduct heat away from the secondthermally conductive layer.
 5. The method of claim 1, wherein the firstthermally conductive layer further comprises at least one of copper,aluminum, iron, chrome, nickel, molybdenum, zinc, silver, gold and tin.6. The method of claim 1, wherein the first thermally conductive layerand second thermally conductive layer maintain an operating temperatureof the photovoltaic cell at or below about 110° C.
 7. The method ofclaim 1, wherein the first thermally conductive layer, second thermallyconductive layer and electrically isolating layer are selected toprevent an electrical breakdown at a voltage up to about 1700 volts. 8.A method of operating a photovoltaic cell assembly, comprising:receiving heat from a photovoltaic cell at a first thermally conductivelayer; reduce a density of the received heat at the first thermallyconductive layer; transferring the heat from the first thermallyconductive layer to a second thermally conductive layer via anelectrically isolating layer that thermally couples the first thermallyconductive layer to the second thermally conductive layer.
 9. The methodof claim 8 further comprising concentrating solar rays at thephotovoltaic cell using a solar concentrator.
 10. The method of claim 8,further comprising spreading heat received from the photovoltaic cellover a lateral area of the first thermally conductive layer to reducethe heat density and conducting electricity from the photovoltaic cellin the first thermally conductive layer.
 11. The method of claim 8,wherein the first thermally conductive layer includes a printed circuitlayer, further comprising electrically coupling the printed circuitlayer to an electrode of the photovoltaic cell.
 12. The method of claim11, further comprising electrically coupling the printed circuit layerto the electrode of the photovoltaic cell via at least one of: a ribbonbond and a wire bond.
 13. The method of claim 11 further comprisingcoupling the printed circuit layer to another photovoltaic cellassembly.
 14. The method of claim 8, further comprising conducting theheat from the second thermally conductive layer to a thermallyconducting backplane that conducts heat substantially away from thesecond thermally conductive layer.
 15. The method of claim 8, whereinthe first thermally conductive layer further comprises at least one ofcopper and aluminum, iron, chrome, nickel, molybdenum, zinc, silver,gold and tin.
 16. A method of generating electricity from a solar panel,comprising: coupling a plurality of photovoltaic cell assemblies via atleast one wire; wherein a photovoltaic cell assembly selected from theplurality of photovoltaic cell assemblies includes: a photovoltaic cell,a first thermally conductive layer configured to receive heat from thephotovoltaic cell and reduce a density of the received heat, a secondthermally conductive layer configured to conduct heat from the firstthermally conductive layer to a surrounding environment, and anelectrically isolating layer configured to thermally couple the firstthermally conductive layer and the second thermally conductive layer;and conducting heat away from the selected photovoltaic cell via thefirst thermally conductive layer, the electrically isolating layer andthe second thermally conductive layer.
 17. The method of claim 16further comprising connecting the plurality of photovoltaic cells toachieve a selected current/voltage ratio.
 18. The method of claim 16,conducting the heat from the second thermally conductive layer to athermally conducting backplane that conducts heat substantially awayfrom the second thermally conductive layer.
 19. The solar panel of claim18, wherein the thermally conductive backplane includes at least one finfor drawing heat from the backplane.
 20. The solar panel of claim 16further comprising enclosing the solar panel in an enclosure thatincludes a Fresnel lens. 21.-40. (canceled)